A coloured plan of part of the Marr Ditch at Purfleet, shewing the sluices, with projected alterations

Plan of the sluice at Purfleet in Essex. A new gunpowder magazine was built on this site in the mid 18th century. Water mills had stood here on the Marr Ditch (now known as the Mardyke) but these had the effect of letting salt water from the river seep into the land. This was thought to be detrimental to the land and so the mills were taken down and new sluices were built as a more efficient drainage system. Wooden floodgates were built to protect the fort from the danger of flooding from the River Thames.